Study of CO interaction with alumina-supported Pd particles

Jungwirthová, I.; Stará, I.; Matolín, Vladimı́r

doi:10.1016/s0039-6028(96)01479-3

Cited by 20 publications

(10 citation statements)

References 8 publications

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“…28 Within the last ten years or so, considerable advances in model systems relevant to heterogeneous catalysis have occurred as a result of modern surface science techniques being able to prepare and characterize dispersed metal crystallites on realistic mimics for catalyst support materials such as silica [29][30][31] or alumina. [32][33][34][35][36] The infrared spectra of adsorbates and probe molecules are accessible on these substrates, 34 as are other techniques such as temperature-programmed desorption ͑TPD͒. 37 Most importantly, such substrates are amenable to investigation by scanning tunneling microscopy ͑STM͒, which means that the surface structure at the atomic level can be determined, making correlations between surface chemistry and surface structure a realistic proposition.…”

Section: Introductionmentioning

confidence: 99%

The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts

Lear

Marshall

López-Sánchez

et al. 2005

The Journal of Chemical Physics

292

188

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Five alumina-supported palladium catalysts have been prepared from a range of precursor compounds [palladium(II) nitrate, palladium(II) chloride, palladium(II) acetylacetonate, and tetraamminepalladium(II) tetraazidopalladate(II)] and at different metal loadings (1-7.3 wt %). Collectively, this series of catalysts provides a range of metal particle sizes (1.2-8.5 nm) that emphasize different morphological aspects of the palladium crystallites. The infrared spectra of chemisorbed CO applied under pulse-flow conditions reveal distinct groupings between metal crystallites dominated by low index planes and those that feature predominantly corner/edge atoms. Temperature-programmed infrared spectroscopy establishes that the linear CO band can be resolved into contributions from corner atoms and a combination of (111)(111) and (111)(100) particle edges. Propene hydrogenation has been used as a preliminary assessment of catalytic performance for the 1 wt % loaded catalysts, with the relative inactivity of the catalyst prepared from palladium(II) chloride attributed to a diminished hydrogen supply due to decoration of edge sites by chlorine originating from the preparative process. It is anticipated that refinements linking the vibrational spectrum of a probe molecule with surface structure and accessible adsorption sites for such a versatile catalytic substrate provide a platform against which structure/reactivity relationships can be usefully developed.

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Section: Introductionmentioning

confidence: 99%

The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts

Lear

Marshall

López-Sánchez

et al. 2005

The Journal of Chemical Physics

292

188

View full text Add to dashboard Cite

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“…As a result some surface studies have returned to study the collection zone idea, though it has also been expressed in different terms as the 'diffusion circle' described above, as a shorthand way of describing the extent of diffusion of a precursor state on the surface [36]. Matolin et al performed a series of elegant experiments by and found a significant enhancement of the sticking of CO on model supported Pd catalysts, using a number of different types of support material [37][38][39][40]. They incorporated this idea of CO mobility into a formulation for the sticking.…”

Section: Precursor States Can ''Seek and Find'' The Active Site On Momentioning

confidence: 99%

The role of precursor states in adsorption, surface reactions and catalysis

Bowker¹

2010

J. Phys.: Condens. Matter

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Among the many concepts which have been developed in surface science and catalysis to explain the nature of adsorption, the role of weakly-held states, socalled precursor states, is one of the most important. The kinetics of precursor-mediated adsorption is described, together with examples showing how significant such effects can be, not just in adsorption itself, but also in surface reactions on crystals and on model supported catalysts. These examples include CO adsorption on Pd single crystals and catalysts and implications for CO oxidation, and extreme examples of the precursor effect, where adsorbate molecules can appear to 'seek out' active sites which are in very low concentration on the surface. The decomposition and oxidation of formic acid is just such an example. Such reactivity patterns then also lead to concepts such as the collection zone' or 'diffusion circle' describing how much of an area of surface is 'swept' by incoming weakly-held molecules during their brief sojourn there.

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“…This value is comparable to the estimates by Matolin and coworkers, who calculated capture zones with DR between 0.5 and 3.3 nm for CO adsorption at 300 K on Pd particles supported on different types of aand g-Al 2 O 3 surfaces. [73][74][75]…”

Section: Size Dependent Co Adsorption Kinetics (Molecular Beam Experi...mentioning

confidence: 99%

Particle size dependent adsorption and reaction kinetics on reduced and partially oxidized Pd nanoparticles

Schalow

Brandt

Starr

et al. 2007

Phys. Chem. Chem. Phys.

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Combining scanning tunneling microscopy (STM), IR reflection absorption spectroscopy (IRAS) and molecular beam (MB) techniques, we have investigated particle size effects on a Pd/Fe(3)O(4) model catalyst. We focus on the particle size dependence of (i) CO adsorption, (ii) oxygen adsorption and (iii) Pd nanoparticle oxidation/reduction. The model system, which is based on Pd nanoparticles supported on an ordered Fe(3)O(4) film on Pt(111), is characterized in detail with respect to particle morphology, nucleation, growth and coalescence behavior of the Pd particles. Morphological changes upon stabilization by thermal treatment in oxygen atmosphere are also considered. The size of the Pd particles can be varied roughly between 1 and 100 nm. The growth and morphology of the Pd particles on the Fe(3)O(4)/Pt(111) film were characterized by STM and IRAS of adsorbed CO as a probe molecule. It was found that very small Pd particles on Fe(3)O(4) show a strongly modified adsorption behavior, characterized by atypically weak CO adsorption and a characteristic CO stretching frequency around 2130 cm(-1). This modification is attributed to a strong interaction with the support. Additionally, the kinetics of CO adsorption was studied by sticking coefficient experiments as a function of particle size. For small particles it is shown that the CO adsorption rate is significantly enhanced by the capture zone effect. The absolute size of the capture zone was quantified on the basis of the STM and sticking coefficient data. Finally, oxygen adsorption was studied by means of MB CO titration experiments. Pure chemisorption of oxygen is observed at 400 K, whereas at 500 K partial oxidation of the particles occurs. The oxidation behavior reveals strong kinetic hindrances to oxidation for larger particles, whereas facile oxidation and reduction are observed for smaller particles. For the latter, estimates point to the formation of oxide layers which, on average, are thicker than the surface oxides on corresponding single crystal surfaces.

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Study of CO interaction with alumina-supported Pd particles

Cited by 20 publications

References 8 publications

The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts

The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts

The role of precursor states in adsorption, surface reactions and catalysis

Particle size dependent adsorption and reaction kinetics on reduced and partially oxidized Pd nanoparticles

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